The present invention relates to a laser module for optical information processing to record or read information recorded onto an optical recording medium such as an optical disc, a photomagnetic disc, or the like, with laser light, and particularly relates to a laser module for dealing with a plurality of wavelengths for the combination of DVD or CD or the like, an optical head and an optical information recording and reproducing apparatus using it.
Recently, a DVD (Digital Versatile Disc) drive using laser light having a wavelength of 650 nm has come into a wide use rapidly as a dual-wavelength drive which is also applicable to CD using laser light having a wavelength of 780 nm. In an optical head used in this drive, semiconductor lasers, collimating lenses, objective lenses, photodetector, etc. are mounted for the respective CD and DVD in order to keep compatibility between DVD and CD. As a result, the number of parts is doubled, and their optical adjustment is complicated, so that the cost increases.
On the other hand, a blue laser having a wavelength of 410 nm has been lively developed, and expected to be put into practical use in the near future. It is therefore necessary to develop a three-wavelength optical head which can also deal with a blue laser while keeping compatibility with CD and DVD. However, preparing and assembling parts for the three wavelengths causes not only a large increase in the cost but also a serious problem in downsizing of the optical head and in ensurance of reliability.
As a technique for miniaturizing such a three-wavelength optical head and ensuring its reliability, JP-A-10-21577 discloses an example of a three-laser module in which three semiconductor laser chips are pasted on a silicon substrate having micro-mirrors and photodetectors, and formed into a module. However, when a deflection/diffraction grating is used in common, a photodetector portion for dealing with the three wavelengths spreads over a wide area. As a result, there occurs a problem that the silicon substrate is made large in size so that the cost is increased. For example, FIG. 5 shows a state of a silicon substrate in which three laser chips each having a chip width of 0.25 mm are arranged. A recess portion on the silicon substrate for arranging the chips therein (hereinafter, referred to as xe2x80x9csink portionxe2x80x9d) is 1.1 mm wide, and focusing and tracking photodetectors corresponding to the respective lasers are disposed on opposite sides of the sink portion. Finally, the width of the silicon substrate reaches 3.9 mm, which is, for example, approximately twice as large as the width of a silicon substrate currently used in a laser module for CD. JP-A-11-134702 disclose a three-wavelength diode for oscillating three-wavelength laser light as a technology corresponding to three-wavelength optical head, and an example for introducing three-wavelength laser light into a common photodetector by using deflector/diffraction grating. However in this situation, two out of three-wavelength are incident into converging optical system in a slanted manner inviting coma aberration.
To solve the foregoing problems, the present invention provides an optical head comprising a plurality of laser light sources and a plurality of photodetectors corresponding to said plurality of laser light sources. The plurality of laser light sources have three kinds of wavelengths A, B and C (A greater than B greater than C), and include first and second laser modules. The first laser module includes laser light sources having the wavelengths A and B and two photodetectors corresponding to the laser light sources having the wavelengths A and B. The second laser module includes a laser light source having the wavelength C and a photodetector corresponding to the laser light source having the wavelength C. Laser light emitted from each laser light source of the first laser module is introduced to an optical information medium through reflection (or transmission) by a wavelength filter. Reflected light from the optical information medium is introduced to the photodetectors of the first laser module. Laser light emitted from the laser light source of the second laser module is introduced to the optical information medium through reflection (or transmission) by the wavelength filter. Reflected light from the optical information medium is introduced to the photodetectors of the second laser module.
Further, in the above-mentioned optical head, a collimating lens, a rise-up mirror and a focus lens are provided as focusing means between the wavelength filter and the optical information medium. In addition, a dichroic mirror is put on a surface of said rise-up mirror, so that light of the wavelength A is transmitted through the dichroic mirror and reflected by a surface of the rising mirror, while light of the wavelength B is reflected by the dichroic mirror.
In addition, the present invention provides an optical head having first and second laser modules. The first laser module includes laser light sources having the wavelengths B and C and two photodetectors corresponding to the laser light sources having the wavelengths B and C. The second laser module including a laser light source having the wavelength A and a photodetector corresponding to the laser light source having the wavelength A. Laser light emitted from each laser light source of the first laser module is introduced to an optical information medium through reflection (or transmission) by a wavelength filter. Reflected light from the optical information medium is introduced to the photodetectors of the first laser module. Laser light emitted from the laser light source of the second laser module is introduced to the optical information medium through reflection (or transmission) by the wavelength filter. Reflected light from the optical information medium is introduced to the photodetector of the second laser module.
Further, in the above-mentioned optical head, a collimating lens, a rise-up mirror and a focus lens are provided as focusing means between the wavelength filter and the optical information medium. In addition, a dichroic mirror is put on a surface of said rise-up mirror, so that light of the wavelength B is transmitted through the dichroic mirror and reflected by a surface of the rise-up mirror, while light of the wavelength C is reflected by the dichroic mirror.
Further, in any one of the above-mentioned optical heads, a beam shaping prism is disposed between the second laser module and the wavelength filter.
In addition, the present invention provides an optical information recording and reproducing apparatus comprising any one of the above-mentioned optical head, optical information medium judging means, and light source selecting means. One is selected from the above-mentioned laser light sources by the light source selecting means on the basis of the result of judgement by the optical information medium judging means.